When transmitting digital data via a line, electromagnetic interference which is proportional to a transmission rate of the data can arise in the region of the line. Conventionally, an increase in the data transmission rate also goes hand in hand with the production of interference signals having higher frequencies. Conventional measures for suppressing such interference include shields and ground surfaces. Since high-frequency signals tend to radiate from the line more readily, their suppression likewise requires greater effort as the frequency of the interference rises. The interference may be radiated from the line in the form of electromagnetic waves or it may propagate along the line.
In order to reduce the required connections between a transmitter and a receiver, a serial transmission of the digital data via the line commonly takes place. At an identical transmission rate, a serial interface must be operated at a faster rate, i.e., at higher frequencies, than a parallel interface, which basically increases the radiation tendency of interference signals at serial interfaces. SPI, I2C, USB, RS232, RS45 and LVDS are typical serial protocols and buses. In a few of these protocols or buses a differential transmission of signals along the conductor is chosen, which doubles the line requirement, but also increases the interference immunity and reduces the emission of interference signals. All of the mentioned protocols or buses use a fixedly predefined data-transmission frequency. Emitted interference signals must therefore be expected only in a frequency band that is able to be defined in advance and is a function of the data transmission rate.
The described interference may also occur in the transmission of measured values from a sensor to a control component. In the environment of motor vehicles, for instance, a sensor together with a multitude of potential electromagnetic interference sources may be used in a widely branched and complex line network. In such an environment, a minimum of interference radiation along or from the line, and resistance to irradiation of electromagnetic interference via the line are usually defined by the specifications of work and services.
In accordance with the present invention, a method and a system are provided for transmitting digital data via a line, which exhibit improved interference characteristics at low expenditure.